Wet dispersion of plant pulp in concrete and use thereof

ABSTRACT

Pulp fibers derived from wood or non-wood plants or recycled paper products are individualized and dispersed in water, and mixed into cement-based mixtures using conventional mixing procedures at relatively low dosages of about 0.3-30 kg of fiber per cubic meter of concrete. Once individualized, the affinity of plant pulp fibers for water facilitates their dispersion in normal cement-based mixtures. Fresh cement-based materials incorporating the dispersed individualized plant pulp fibers provide desirable workability, resistance to segregation and bleeding, pumpability, finishability, and reduced rebound when pneumatically applied. Hardened cement-based materials incorporating the dispersed individualized plant pulp fibers provide improvements in crack resistance, toughness, impact resistance, fatigue life, abrasion resistance, and other mechanical, physical and durability characteristics.

CROSS REFERENCES TO RELATED APPLICATIONS

Continuation of Ser. No. 08/558,847, Filed Nov. 15, 1995 U.S. Pat. No.5,643,359.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY-SPONSOREDRESEARCH AND DEVELOPMENT

Rights to this invention fully belong to DPD, Inc. of Lansing, Mich.

BACKGROUND

1. Field of Invention

This invention relates to brittle matrix composites and plant pulp, andespecially to the processing and use of pulp fibers for reinforcingcement-based materials.

2. Description of the Prior Art

The concept of using fibers to improve the behavior of buildingmaterials is old; examples include adding straw fibers to sun-dried mudbricks (adobe) and asbestos fibers to pottery, thus creating a compositewith a better performance. Such performance could be translated in thecase of adobe by a better resistance to cracking and a better resistanceto fragmentation after cracking induced by repetitive changes intemperature and humidity. It is no surprise that when Portland cementconcrete started evolving as a building material, attempts were made toadd fibers to it to improve its behavior. Early work in this area in the19^(th) century led to the development of ferrocement and reinforcedconcrete as known today. However, the use of continuous reinforcementrequired careful placement and higher labor technical skills, hencehigher cost.

The idea of using strong discontinuous fibers as reinforcement forconcrete has been a challenge to many civil engineers. Adding thereinforcement to the mixer in the form of fibers, simply like addingaggregates or admixtures, to create a homogeneous, isotropic, andmoldable structural material is a dream that started more than a centuryago, and is still in the making today. The fibers considered for thereinforcement of concrete include steel, polypropylene, nylon, glass,carbon, kevlar, and natural fibers. A selective number of patens in thefield of cellulose fiber reinforced cement-based materials, which is thesubject of this invention, is reviewed next. A listing of the referencesis first presented followed by a brief discussion of same.

U.S. PATENT DOCUMENTS

U.S. Pat. No. 3,753,749 to Nutt (1971)

U.S. Pat. No. 4,369,201 to H. Kober (1983)

U.S. Pat. No. 4,400,217 to H. Kober (1983)

U.S. Pat. No. 4,985,119 to K. D. Vinson and B. J. L. Huff (1991)

U.S. Pat. No. 5,102,596 to Lempfer et al. (1992)

FOREIGN PATENT DOCUMENTS

None.

OTHER PRIOR ART

None.

REVIEW OF THE ABOVE LITERATURE

Modern innovations and commercial activities relevant to plant fiberreinforced cement composites largely focus on the use of softwood kraftpulp as replacement for asbestos in thin cement products. In thisapplication, kraft pulp fibers are used at relatively large volumefractions (about 20%) in cement mixtures with relatively low dosages ofvery fine aggregates. In order to facilitate the dispersion of such highvolume fractions of kraft pulp fibers, excess amounts of water are usedin the mix to form a fluid slurry; subsequently, the excess water isremoved from the slurry using suction. The production process (refereedto as Hatschek or slurry-dewatering) is highly specialized and isapplicable only to controlled production facilities. The end productsare in the form of thin-sheet products. U.S. Pat. No. 4,985,119 to K. D.Vinson and B. J. L. Huff(1991) describes a development in the use ofsoftwood kraft pulp in slurry-dewatered thin cement products where thesoftwood kraft pulp has higher fractions of summerwood fibers thannaturally occur in trees n order to provide a higher reinforcementefficiency. U.S. Pat. Nos. 4,369,201 and 4,400,217 to H. Kober (1983)also relate to the use of relatively high volume fractions of plantfibers for the replacement of asbestos in thin cement productsmanufactured using specialized processing techniques. Anotherspecialized processing of cellulose fiber cement is presented in U.S.Pat. No. 5,102,596 to Lempfer et al. where a milled mixture of cellulosefiber, cement and water is shaped into a mold through pressing. Ourinvention is distinguished from U.S. Pat. No. 4,985,119, 4,369,201 and4,400,217 because we use: (1) relatively low volume fractions of plantpulp fibers as secondary reinforcement (instead of high volume fractionsof fibers as primary reinforcement); (2) conventional concrete mixtureswhich are built into conventional concrete products such as pavements,floor systems, etc. (instead of mortar mixtures with fine sand or withno sand which are built into thin building products); (3) conventionalmixing techniques and equipment where the low intensity of the mixingeffort and the shortage of moisture complicate the dispersion of plantpulp fibers (instead of specialized processing techniques such as theslurry-dewatering procedures which make excessive moisture and mixingeffort available for the dispersion of fibers).

U.S. Pat. No. 3,753,749 to Nutt (1971) teach the use of cellulose fiberswhich have been dried following the common practice of the paperindustry relying heavily on pressing, accompanied with heating, to drythe wet pulp into a dense dried pulp with strong fiber-to-fiber bonding.Such strong fiber-to-fiber bonding necessitates the use of intensemechanical action to break the fiber bonds and make somewhat individualfibers available for dispersion in cement-based materials. The intensityof mechanical action in this process of separating fibers from eachother causes damage and breakage of fibers which reduce theirreinforcement efficiency in cement-based materials. Our inventioninvolves the use of cellulose fibers which have been specially processedto achieve reduced fiber-to-fiber bonding and thus allow separation intosubstantially individual fibers using lower-intensity mechanical actionwhich reduces the damage and breakage of fibers. More specifically, thewet cellulose pulp is initially dried with less reliance on pressinginto fluff pulp. The subsequent mechanical separation of the fluff pulpinto substantially individual fibers can be performed using relativelylow amounts of mechanical energy and with limited damage to fibers.

OBJECT OF THE INVENTION

It is therefore an object of our invention to provide procedures foruniform dispersion of plant pulp fibers in conventional concretemixtures using conventional mixing procedures and equipment.

It is another object and advantage of our invention to provide alow-cost and effective secondary reinforcement system for concreteconsisting of relatively low volume fractions of uniformly dispersedplant pulp fibers which are compatible with and develop sufficientbonding to the concrete matrix.

It is a further object and advantage of our invention to providereinforcing fibers for concrete which desirable fresh mix workability,segregation and bleeding resistance, pumpability, finishability andplastic shrinkage cracking resistance, and reduced rebound whenpneumatically applied.

It is yet a further object and advantage of our invention to enhance thedrying and thermal shrinkage cracking resistance, impact and abrasionresistance, fire resistance, toughness, and other mechanical physicaland durability characteristics of hardened concrete products withdispersed plant pulp fibers at relatively low volume fractions.

Still further objects and advantages will become apparent from aconsideration of the ensuing description.

SUMMARY OF THE INVENTION

According to the present invention there is disclosed a method ofproviding concrete with an effective and low-cost secondaryreinforcement system, comprising individualization of untreated ortreated pulp fibers of about 0.1-30 mm in length, about 0.001-0.1 mm indiameter and having length-to-diameter ratios of about 30-3000, derivedby at least one of chemical, mechanical or thermal means, orcombinations thereof, from at least one of non-wood plants, softwoods,hardwoods and recycled paper products, with the individualizationprocess taking place in about 5-100% of mixing water using mechanicalaction for reducing the bonding between fibers so that they can bedispersed in conventional concrete mixtures using conventional mixingequipment at relatively low dosages of about 0.3-30 kg per cubic meter.The affinity of individualized pulp fibers for water facilitates theirdispersion in concrete. The fresh concrete mixtures incorporatingdispersed plant pulp fibers possess desirable workability, resistance tosegregation and bleeding, pumpability, finishability, resistance toplastic shrinkage cracking, and reduced rebound when pneumaticallyapplied. The hardened concrete materials incorporating dispersed plantpulp fibers show improvements in cracking resistance, tensile andflexural strength, toughness characteristics, impact resistance,abrasion resistance and other mechanical, physical and durabilitycharacteristics when compared with plain concrete. These improvementsresult from the fine and slender geometry and desirable mechanical,physical and durability characteristics of plant pulp fibers and theircompatibility with concrete, and are achieved at relatively low cost dueto the cost-competitiveness of plant pulp fibers. Precast andcast-in-place as well as reinforced and plain concrete and shotcretebenefit from such improvements in fresh and hardened materialproperties.

BRIEF DESCRIPTION OF THE DRAWINGS

None.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Plant pulp is derived from wood or non-wood plants through pulpingprocesses which use at least one of mechanical, thermal and chemicalprocesses. Recycled paper is another source of pulp. Conventionalpulping processes yield suspensions of pulp fibers at low concentrationsin water, which are subsequently dried by the application of pressureand heat. The resulting dried pulp is largely used in paper andabsorbent products. Paper products are generally made by individualizingthe fibers in water and forming them into the final product. Absorbentproducts are typically produced by milling of the dried pulp intoindividual fibers which are formed into the final product.

Cellulose fibers possess desirable properties for the reinforcement ofcement-based materials. They offer relatively high levels of tensilestrength and elastic modulus with a relatively high ratio of length toequivalent diameter. Cellulose fibers also offer a relatively high fibercount per unit weight--of the order of few million fibers per gram. Thishigh fiber count strongly benefits the reinforcing action of cellulosefibers in cement-based materials if they are uniformly dispersed withinthe cement-based matrix. The strong tendency of cellulose fibers todevelop hydrogen bonding between each other, however, complicates theiruniform dispersion in conventional cement-based materials where limitedmixing water and energy is available to individualize fibers. One optionis to dry the fibers so that the extent of hydrogen bonding betweenfibers is reduced, and to first disperse these fibers in at least afraction of the mixing water using more mechanical effort thanconventional mixing of water makes available. It is preferable to useall the water to be added to the cement-based material in this wetprocess of individualizing fibers. This step of dispersing the pulp intosubstantially individual fibers in water may also be performed withother mix ingredients such as cement and admixtures added to the water.The mechanical action for individualizing the fibers may be in the formof blending or milling action or in other forms capable of separatingthe pulp into substantially individual fibers. This mechanical actionmay simply separate the fibers or may also impart some fibrillationaction which roughens the fiber surfaces and increases their mechanicalbond strength to cement-based materials.

The resulting individualized fibers would be added to conventionalcement-based materials, together with the mixing water in which theywere dispersed, at any stage during the mixing process. Suchconventional cement-based materials comprise about 0.3-30 kg per cubicmeter of cellulose fiber, about 50-1500 kg per cubic meter ofcementitious material, about 51-1000 kg per cubic meter of water, andabout 100-3600 kg per cubic meter of aggregate, and optionally differentchemical, mineral, polymeric and air-entraining admixtures. Suchcementitious material is any hydraulic cement, including Portlandcement, blended cement, masonry cement, set regulated cement,high-alumna cement, and expansive cement. The aggregates could benatural, crushed stone, or other forms of artificial or naturalnormal-weight, light-weight or heavy-weight aggregates.

Conventional mixing action of cement-based materials would provide foruniform dispersion of fibers within the material system. Suchconventional mixing action may be performed in a rotary drum mixers, panmixers, mortar mixers, continuous mixers, and ready-mixed concretetrucks; manual mixing is also a possibility. The individualized fibersand other ingredients of the cement-based material can be added in anysequence to the mix. For example, the individualized fibers could beadded to the cement-based material after all other ingredients have beenmixed. The addition of fibers followed by the continuation of mixingwould uniformly disperse the fibers within the cement-based material.

The fresh cement-based materials incorporating cellulose fibers can behandled, pumped, shot (pneumatically in shotcrete applications), placed,consolidated, finished and cured using the same procedures and equipmentapplicable to conventional cement-based materials. The presence ofcellulose fibers in fresh cement-based materials at dosages of about0.5-5.0 kg per cubic meter benefits certain aspects of the workabilityof fresh cement-based mixtures, including their finishability.

Curing of cellulose fiber reinforced cement-based materials, by anyconventional technique applicable to normal cement-based materials suchas moist curing, steam curing, high-pressure steam curing or applicationof a curing membrane, yields a hardened cellulose fiber reinforcedcement-based material. The presence of cellulose fibers in this hardenedmaterial causes improvements in microcrack and crack resistance,strength, toughness, impact resistance, abrasion resistance and variousaspects of the physical, mechanical and durability characteristics ofthe cement-based materials. The hydrophobic nature of cellulose fibersurfaces and their potential for hydrogen bonding to cement-basedmaterials benefit their reinforcing action in hardened cement-basedmaterials. Cellulose fibers, also being of roughly the samecross-sectional dimensions as cement particles, do not interfere withdense packing of cement particles; this favors the microstructural andengineering characteristics of the hardened material.

EXAMPLE 1

We added 15 kg of tap water to 120 g of softwood (southern pine) kraftfluff pulp and blended them for 60 seconds in a blender in order todisperse the fibers in water. We added this dispersion of pulp fibers inwater to 40 kg of Type I Portland cement and 120 kg of natural concretesand (with 4.75 mm maximum particle size) and mixed them in a rotarydrum mixer for five minutes. Companion mixtures were also prepared undersimilar conditions but without the use of cellulose fibers. We cast themixtures into prismatic steel molds of 25 mm thickness, 57 mm width and250 mm length. The mixtures in molds were covered with wet burlap. Thespecimens were demolded after 24 hours, cured at 100% relative humidityand 20° C. temperature for 14 days and then air-dried until the test ageof 28 days. They were then tested in flexure under four-point loadingover a span of 171 mm, with loads applied at 57 mm from each endsupport. The peak load at failure was recorded. Three specimens weretested for each mix. The average peak load for the mix with cellulosefibers corresponded to a stress of 2.4 MPa, compared with 1.8 MPa forthe mix without cellulose fibers. Observation of failure surfacesindicated that cellulose fibers were uniformly dispersed in thecement-based material.

We claim:
 1. A process of making cellulose fiber reinforced cement-basedmaterial using cellulose pulp from at least one of softwoods, hardwoodsor non-wood plants, said pulp being derived from at least one ofmechanical, thermal or chemical pulping methods, the processcomprising:a. drying wet cellulose pulp resulting from the pulpingmethods, wherein the drying is accomplished by applying at least one ofheat or pressure to the fibers; b. adding to the cellulose pulp about5-100% mixing water and mechanically separating the pulp into individualfibers; c. adding the separated fibers to a cement-based material at adosage ranging from about 0.3-30 kg per cubic meter of cement-basedmaterial, said cement-based material further including about 50-1500 kgof cementitious material per cubic meter, about 50-1000 kg of water percubic meter, and about 100-3600 kg of aggregate per cubic meter; and d.mixing the separated fibers into the cement-based material so as todisperse the fibers uniformly throughout the cement-based material. 2.The process of claim 1, wherein the said step of drying wet pulp throughthe addition of at least one of heat or pressure takes place underconditions to achieve a dried fluff pulp with low fiber-to-fiber bondingtherein.
 3. The process of claim 1, wherein said fibers are added tosaid cement-based material at a dosage of 0.5-5.0 kg per cubic meter. 4.The process of claim 1, wherein said cement-based material furtherincludes at least one of chemical admixtures, mineral admixtures,polymeric admixtures, or air entraining agents.
 5. The process of claim4, wherein at least one of cement, chemical admixtures, mineraladmixtures, polymeric admixtures, air-entraining agents, or aggregatesare mixed with fibers and water in the step of mechanically separatingthe fibers.
 6. The process according to claim 1, wherein the time ofmixing of the separated fibers into the cement-based material exceeds 20seconds.
 7. The process according to claim 1, wherein said aggregatecomprises mineral, synthetic, metallic, or organic aggregate, having aparticle size of between about 0.05-100 mm.
 8. The process according toclaim 1, wherein said mechanical separating step comprises agitating thefibers in water.
 9. The process according to claim 1, wherein saidmechanical separating step comprises milling the fibers in water. 10.The process of claim 1, wherein said mechanical separating stepcomprises fibrillating the fibers in water.
 11. The process according toclaim 1, wherein said mechanical separating step comprises carrying thepulp in a high-speed water stream and impacting the water stream andpulp against a solid surface.
 12. The process of claim 1, wherein thewet cellulose pulp comprises waste paper products.
 13. The process ofclaim 1, wherein said cement-based material is mortar having a maximumaggregate particle size of less than 5 mm.
 14. The process of claim 1,wherein said cement-based material of step (d) is further subjected toat least one of pumping, casting, consolidating, pneumatic application,finishing, or curing processes.
 15. The process according to claim 1,wherein said drying step further comprises chemically treating thecellulose pulp to produce a dried softened fluff pulp with lowfiber-to-fiber bonding therein.
 16. The process of claim 15, whereinsaid chemical treating comprises the use of at least one of asurfactant, a high bulk additive, or a sizing agent.
 17. A freshconcrete mixture having dispersed therein separated cellulose pulpfibers the concrete mixture comprising:0.3-30 kg per cubic meter offibers, wherein the fibers are produced by drying a wet cellulose pulpby applying at least one of heat or pressure, and subsequently adding tothe cellulose pulp about 5-100% of mixing water and mechanicallyseparating the wet pulp into fibers; about 50-1500 kg per cubic meter ofcementitious material; about 50-1000 kg per cubic meter of water; about100-3600 kg per cubic meter of aggregate; and wherein the fibers aredispersed uniformly throughout the cement-based material through mixingfor a sufficient period of time.
 18. A fresh concrete mixture accordingto claim 17, wherein the drying of the wet pulp comprises theapplication of at least one of heat or pressure under conditions toachieve a dried fluff pulp with low fiber-to-fiber bonding.
 19. A freshconcrete mixture according to claim 17, wherein said mixture comprises0.5-5.0 kg per cubic meter of the cellulose fibers.
 20. A fresh concretemixture according to claim 17, further including at least one ofchemical admixtures, mineral admixtures, polymeric admixtures, orair-entraining agents.
 21. A fresh concrete mixture according to claim17, wherein said cellulose fibers have been chemically treated by theuse of at least one of a surfactant, a high bulk additive, or a sizingagent.
 22. A hardened cellulose fiber reinforced cement-based structurecomprising:about 0.3-30 kg per cubic meter of cellulose fibers, whereinthe fibers are produced by drying a wet cellulose pulp by applying atleast one of heat or pressure, subsequently adding to the cellulose pulpabout 5-100% mixing water and mechanically separating the wet pulp intofibers; about 50-1500 kg per cubic meter of cement; about 50-1000 kg percubic meter of water; about 100-3600 kg per cubic meter of aggregate;and said cellulose fibers being uniformly dispersed throughout thehardened structure through mixing of the fibers together with thecement, water and aggregate for a sufficient length of time prior tocuring.
 23. A hardened cellulose fiber reinforced structure according toclaim 22, wherein the drying of the pulp comprises the application of atleast one of heat or pressure under conditions to achieve a dried fluffpulp with low fiber-to-fiber bonding.
 24. A hardened cellulose fiberreinforced structure according to claim 23, wherein the structurecomprises 0.5-5.0 kg per cubic meter of the cellulose fibers.
 25. Thehardened cellulose fiber reinforced cement structure of claim 23,wherein said cellulose fibers have been derived from at least one ofsoftwood, hardwood or non-wood plants through at least one ofmechanical, thermal, or chemical pulping processes, and have a lengthranging from 0.1-30 mm, a diameter ranging from 0.001-0.1 mm, and a meanlength-to-diameter ratio ranging from 30-3000.
 26. The hardenedcement-based structure according to claim 22, further including at leastone of chemical admixtures, mineral admixtures, polymeric admixtures, orair entraining agents.
 27. The hardened cement-based structure of claim22, further including a gas-forming agent and air bubbles therein. 28.The hardened cement-based structure according to claim 22, furtherincluding at least one of continuous or discrete reinforcement inaddition to the cellulose fibers.
 29. The hardened cement-basedstructure of claim 22, wherein said cellulose fibers have beenchemically treated by the use of at least one of a surfactant, a highbulk additive, or a sizing agent.